1. Field of the Invention
This invention relates to the compensation of the drift of the output signal of a photoelectric sensor and, more particularly, to the compensation of the drift of the output signal of a photoelectric sensor included in a proportional electric remote control apparatus of the manipulation or analog type comprising sliding pressure sensors pairwise associated and selectively actuated by an actuation part or actuation member for progressive displacement, which each pressure is being functionally associated with a photoelectric sensor adapted to produce an electrical signal of which one parameter is representative of the displacement and/or position of the pressure sensor, and hence, of the actuation member.
2. Description of Related Art
The characteristics of the operation of a photoelectric sensor are subjected to an evolution which corresponds to two types of drifts.
A first cause of drift is imputed to variations of the ambient temperature. This drift can be very important, for instance, the drift of an electroluminescent diode (LED) can be in the range +40% to -60% around a nominal value when the temperature varies between -40.degree. C. and +85.degree. C.
A second cause of drift is imputed to aging of the constituents or components of the sensor. This aging depends on the materials used for the sensor or its constituents, or its fabrication, or the life of the sensor, and also, or the temperature, such that the evolution of the aging and the drift of the output signal of the sensor which results therefrom are difficult to foresee, as they are all characteristic of each sensor.
It is therefore necessary to proceed in a periodic manner with a recalibration, regauging, etc. . . . of a sensor to be in a position to know the true value of its output signal.
These considerations are of general character and apply to all types of photoelectric sensors, including sensors formed by a photoemitter/photoreceiver pair (for example photodiodes) between which a movable part with variable transparency is located. Thus it is possible to form a proportional remote control in which one parameter (for example the current amplitude or the voltage) of the output signal of the photoreceiver translates the displacement of a command part (for example a displaceable handle) in view of the command of a provided utilizing part.
In such a mounting, a drift of an output signal of the photoelectric sensor can be translated like a superposition of a true signal and a parasitic signal having the same effect as an actuation of the command part and can entrain a non-desired actuation of the provided utilizing part.
Hence it appears indispensable to assure a reliable command of the provided utilizing part to compensate the output signal of the photoelectric sensor essentially as a function of aging and of the temperature and equally in the measurement of other possible causes, and in particular regarding the appearance of a dark signal (output signal of the photoelectric sensor when it is not optically excited).